Gravitational interactions occasionally eject small bodies from the solar system, and this process is thought to have been particularly common while the system was first forming. The same thing should have occurred around other stars, casting comets and asteroids into interstellar space, but no such interstellar objects have been identified. Meech et al. discovered a small object, now formally designated 1I/2017 U1 ('Oumuamua), whose trajectory indicates that it arrived from interstellar space. Changes in its brightness demonstrate that 'Oumuamua is rotating and is several times longer than it is wide. 'Oumuamua is quickly passing through the solar system and soon will resume its interstellar journey.